Selective interference during the retrieval of visual images

Twenty-six subjects memorized lists of (low I and high I) noun pairs under imagery or verbal mediation instructions. At recall the subjects were presented a digit (“1” or “2”) either auditorily or visually as an interfering stimulus.

Visual interference was found to selectively affect the retrieval of high I response terms. Also, the retrieval of nouns studied by imagery mediation was found to be selectively disrupted by visual interference.

These results suggest that the qualities of a visual image are retained all the way from image acquisition to retrieval, and that the visual components of images generated at the acquisition stage are probably not lost by subsequent coding processes.     

A note on further experiments on the effects of meprobamate on discrimination performance in the monkey

A previous experiment (Gross and Weiskrantz, 1961) has shown that performance on a successive auditory discrimination task is impaired by injections of meprobamate. The present two brief experiments indicate that the drug also impairs simultaneous visual discrimination performance, although not to the same degree as found earlier for auditory discrimination. The original finding, therefore, cannot be attributed simply to unique features of the auditory discrimination situation, such as the “go—no-go” response contingency. Since neither overtraining nor drug habituation appears to be of great importance, it is suggested that the lesser effect of the drug in these experiments reflects the greater stability of visual than auditory habits in the monkey.

Earlier work has shown that meprobamate and reserpine can cause a severe deterioration in auditory discrimination performance of monkeys (Gross and Weiskrantz, 1961). This result was taken as supporting a hypothesis, growing out of still earlier research, that tranquillizers decrease the utilization of sensory information (Weiskrantz and Wilson, 1956; Weiskrantz, 1957).

The auditory task, as is almost always the case with monkeys as subjects, involved a “go—no-go” type of response contingency—i.e. the animal had to respond to the positive stimulus and had not to respond to the negative stimulus in order to achieve reward. It might be objected, therefore, that the deterioration in performance was associated not with discrimination as such but with the animals' willingness to perform at all. In fact, it was found that the animals tended to make most of their errors under the drugs by responding when they should not rather than not responding when they should.

The purpose of the present experiments, therefore, was to test the animals with a visual discrimination task in which both the positive and negative stimuli were presented simultaneously. An effect of the drug could not, in this situation, be characterized simply as altering the responsiveness of the animal. A further purpose in using visual stimuli was to test the generality of the earlier finding in a sense modality other than audition.     

Selective strategies in the assimilation of successively presented signals

It is found that performance in experiments on the psychological refractory period is highly affected by instructions. In the present experiment subjects were instructed either to handle the signals successively or to group them. Both instructions were obeyed. This seems to indicate that the human organism has various strategies available. Which strategy is actually applied is likely to depend on the structure of the experimental situation, and partly also, on momentary preference. This may explain the variety of results in the literature on this subject.

Finally, it is found that, when two signals are presented simultaneously, the total reaction time is considerably shorter if the signals are “grouped” than if they are “handled successively.” This difference disappears at interstimulus intervals of 0.2 sec. and 0.4 sec. The hypothesis is put forward, that the gain in time at the former case is due to simultaneous perceptual processing of the signals.     

Information relevance, working memory, and the consideration of alternatives

People routinely focus on one hypothesis and avoid consideration of alternative hypotheses on problems requiring decisions between possible states of the world--for example, on the “pseudodiagnosticity” task (Doherty, Mynatt, Tweney, & Schiavo, 1979). In order to account for behaviour on such “inference” problems, it is proposed that people can hold in working memory, and operate upon, but one alternative at a time, and that they have a bias to test the hypothesis they think true. In addition to being an ex post facto explanation of data selection in inference tasks, this conceptualization predicts that there are situations in which people will consider alternatives. These are:

1. “action” problems, where the alternatives are possible courses of action;

2. “inference” problems, in which evidence favours an alternative hypothesis.

Experiment 1 tested the first prediction. Subjects were given action or inference problems, each with two alternatives and two items of data relevant to each alternative. They received probabilistic information about the relation between one datum and one alternative and picked one value from among the other three possible pairs of such relations. Two findings emerged; (1) a strong tendency to select information about only one alternative with inferences; and (2) a strong tendency, compared to inferences, to select information about both alternatives with actions.

Experiment 2 tested the second prediction. It was predicted that data suggesting that one alternative was incorrect would lead many subjects to consider, and select information about, the other alternative. For actions, it was predicted that this manipulation would have no effect. Again the data were as predicted.     

Temporal structure of letter groups and span of perception

The span of perception for letter groups depends on number of letters presented, length of presentation and structure of the groups. The experiment reported varied the temporal structure of the groups, leaving the total number of letters constant. Groups of 12 letters were presented as a whole or in two or more successive “units.” The total time of presentation was 1-5 sec. In the first experiment each unit was visible until the next appeared, in the second experiment units were visible only during 1/4 sec., although intervals between successive units were kept constant.

The following conclusions emerged:

(a) The visual presence of units did not affect the reproduction for durations over 0.25 sec., except in the 12-letter presentations.

(b) 2×6 letters gave better results than either simultaneous presentation or other divisions; temporal separation was 0.75 sec.

(c) Higher order approximations to Dutch have more influence on 3 × 4, 2 × 6 and 1 × 12 letters than on 4 × 3 and 6 × 2 letters.

(d) A serial order effect exists: central units are reproduced less well than first and last units.

It is suggested that handling a fixed amount of information within a fixed period is limited on the one hand by confusion between simultaneous elements and on the other hand by the interaction between successive units presented too rapidly to allow for proper operation of immediate memory.

The difference between span of perception and span of memory is stressed.     

Voluntary attention in peripheral vision and its effects on acuity and differential thresholds

The three experiments described in this paper were intended to show whether voluntary attention to a particular part of the peripheral visual field had any effect on the accuracy of the subject's perception. Test objects near to threshold value (for acuity or for changes in luminance) were used. The experiments were also designed to study the possible distracting effect of other stimuli presented simultaneously in different parts of the field.

In Experiment 1 the subject could be given foreknowledge of the position in which an acuity test object would appear. In Experiment 2 the signal of where to attend was given simultaneously with the exposure of an acuity test object. In Experiment 3 differential thresholds for luminance were investigated by methods similar to those used in Experiment 2.

It was found in all these cases that the instructions to attend to a particular part of the peripheral field had no significant effect on perception unless there were simultaneously exposed “competing” stimuli in other parts of the field. The results support the view that, in peripheral vision, attention acts selectively on the immediate memory trace only when there is a complex pattern of stimulation.     

Experimental disorientation in the horizontal plane

Twenty-eight subjects were examined on a visual matching task for their ability to maintain an orientation with respect to a particular direction in the horizontal plane following a voluntary rotary body movement through 180 degrees. Each subject was examined with respect to eight different directions.

Numerous gross errors occurred when visual information was reduced to the display of an arrow indicating a direction and a second arrow manipulated by the subject. The magnitude and distribution of the errors suggest that, under the conditions of this experiment, visual information as to direction in the horizontal plane is analysed according to the two horizontal dimensions defined by the sagittal and coronal planes of the head. In correcting for the rotary body movement, failure may occur with respect to either or both of these two dimensions. The frequency of a failure to make any correction at all (i.e. 180-degree errors) is consistent with independent failure in each of the two horizontal dimensions.

Failure is markedly more frequent in the fore-aft dimension than in the left-right dimension. It is suggested that this may be explained in terms of the ambiguous spatial significance of vertical disposition on the retina and the possibility of contamination between the two systems of conceptual analysis which identify the vertical and the fore-aft dimensions of visual space.

It is demonstrated that when minimal “landmarks” are provided they tend to be utilized as reference points in attempts to maintain orientation, even when the subject is aware that the “landmarks” are misleading. Such a use of “landmarks” does not suppress the previously mentioned mechanism of dimensional orientation.

The relevance of these results to normal human orientation is discussed.     

Temporal factors in pattern vision

A sequence of uncorrelated randomly patterned visual stimuli (“visual noise”) is normally seen as a field of particles in “Brownian motion.” When each frame of the sequence is followed by a blank flash superimposed on the same region of the visual field, the apparent structure of the noise field is strikingly altered, its form varying with the time interval between frame and flash. At a critical interval, many dots seem to cohere, to form maggot-like objects.

Some of the factors determining this critical interval have been studied. They include the brightness, repetition frequency and exposure duration of the noise field, and the distance of its retinal image from the fovea.

The critical interval for “perceptual blanking” is quite different from that for the “maggot effect,” but the two show a suggestively similar dependence upon the duty cycle of the noise display.

It is of some neurological interest that the phenomenon is not appreciably visible with dichoptic mixing of noise and blank stimuli.     

Driye-leyel and flexibility in paired-associate nonsense-syllable learning

“High-anxiety” and “low-anxiety” subjects, selected for extreme scores on the Taylor Anxiety Scale, learned a list of paired-associate nonsense syllables in the belief that they were undergoing an intelligence test. Both groups were then given a second list of paired associates to learn, the stimulus-items being the same as those of the first list but the responses being changed. Before the presentation of the second list, half the subjects in each group were given anxiety-increasing instructions and the remaining half were given reassuring instructions.

The results verified two predictions made from Hull's behaviour theory, using the concept of fear or anxiety as a secondary drive:—“high anxiety” subjects took more trials to master the second learning task than “low-anxiety” subjects; and there was a significant interaction between initial anxiety-level and type of instructions, such that “high-anxiety” subjects who received drive-increasing instructions had a worse performance in the second part than all other sub-groups. There was no indication that “low-anxiety” subjects were significantly affected by the type of instructions received. The “high-anxiety” group had greater difficulty than the “low-anxiety” group in learning the first list, but the difference was non-significant.     

Visual search without eye movement

Two experiments have been made on the problem of visual search using six patterns which were geometrically simple, and familiar to the subject.

In each case the subject's task was to say where, among the complex of patterns, a particular pattern (the “test object”) appeared when the exposure of the whole display was so brief as to prevent scanning by the eyes. He could be informed visually (in Experiment I) or verbally (in Experiment II) which pattern was to be regarded as the “test object.”

In both experiments it was found that foreknowledge of what was to be the test object gave a significantly higher standard of accuracy than knowledge given later. This suggests that something analogous to visual search can occur without eye movements.     

Changes in behaviour associated with a nervous system poison (DDT.)

The main purpose of the investigation was to show that behaviour measures can be used to investigate the effects of those toxic drugs which produce “biochemical lesions” in the nervous system although the nature of the lesions still remains undetermined. The advantages of this approach are twofold. First, a psychological study may help to uncover the initial effects of the drug, and thus provide evidence which may lead to the ultimate understanding of the action of the drug. Second, and of value from the practical point of view, such a method may be used to detect toxicity.

In this study D.D.T. was used. Two experiments were performed on one control and four experimental groups of albino rats. Problem solving behaviour, speed and pattern of locomotion, and reaction to stress involving visual stimuli were observed.

Problem solving behaviour was found to be unaffected by the drug; no changes were found in speed of locomotion, but pattern of locomotion revealed that “ataxia” was one of the initial effects of D.D.T. poisioning. The experimental animals were found to be generally less reactive to “stress”; “hyper-irritability” reported in previous studies being explicable in terms of exaggerated motor responses.

The results obtained on “ataxia” showed that the procedure adopted here could be used to detect chronic D.D.T. toxicity in rats.     

A further study of the pendulum phenomenon

A first series of experiments had demonstrated certain conditions eliciting or inhibiting a “pendulum” phenomenon in the visual perception of apparent movement. The present study consists of five further variations designed to show more clearly conditions of occurrence and non-occurrence of this type of movement. The main findings are:

(i) Altering the axis of display to vertical significantly reduces the frequency of pendular-movement perception;

(2) Altering the position of metronome from behind to the side of the visual display, gives results almost identical with those where the metronome was inaudible, but, when the metronome is illuminated in this position, all forms of movement perception are reduced, and no pendular movement is reported.

The results for all the ten conditions, including the five of the first series are summarized, and the following possible factors are discussed: past experience, physiological nystagmus, and intervening adaptation. All three may be required to account for the perceptual phenomena under investigation and the dichotomizing of explanations into “experiential,” or “physiological,” appears to be arbitrary and inconsistent with the complexity of the observed facts.     

like and cross modality recognition in subnormal children

The ability of mentally subnormal children to recognize previously presented visual or verbal stimuli was compared. In “like-modality” procedures they had to recognize words or pictures in the modality in which they had originally been presented. In “cross-modality” procedures the stimulus they had to recognize was in the opposite modality from that which had been used for the first presentation.

In every recognition test the items had to be recognized from among an equal number of novel stimuli. Cross-modality procedures resulted in higher recognition scores. The hypothesis is advanced that this could be accounted for by the necessary translation from one type of sensory image to another in the cross-modality trials, which might minimize over-generalization.     

Do visual images have gestalt properties?

Recent research has demonstrated that percepts and images share processing resources. A natural consequence of this evidence is to ask what kind of properties are shared by the two representational systems, i.e. images and percepts. To what degree, for example, do images share the complex organization of visual percepts?

This paper investigates whether percepts and images share Gestalt properties. Four experiments were conducted to study this hypothesis. In all experiments subjects were presented with an auditory message in which approximately 15 locations in a matrix were defined by giving the co-ordinates of the cells. Half of the stimuli presented some “good” form, whereas in the other half the locations of the pieces were scattered. Subjects were systematically less able to recall the locations of the random forms. Therefore, it could be argued that the “good” forms help in image construction, even though the elements were auditorily presented. Effects of varying presentation speed, order, and of requiring a mental rotation before recall support this conclusion.     

Phenomenal causation at a distance

The aim of this research was to study the finding by Michotte, that a moving object A can apparently produce movement in a projectile B without making contact with it.

The experiments confirm the existence of a causal impression of “pushing at a distance,” but they demonstrate that the greater the distance the smaller the chance that this impression will occur.

When it does, in fact, occur, it has the same characteristics, and is associated with the same experimental conditions, as the impression of “pushing with contact.”

Temporal continuity must obtain between the stopping of the moving object and the starting of the projectile; this refutes any theory positing that there is a “passage” of movement from one object to the other. The effects of differences in speed of movement, whether absolute or relative, are similar in both instances.

In general, however, it appears that distance slightly accentuates the segregation of the movements and that the temporal and kinematic conditions of integration require to be more favourable in the case of distance, if an impression of pushing is to be given which is as satisfying as that found in the case of direct contact.

The size of the Radius of Action, that is, the extent of the passive phase of the projectile, is of the same order in the two cases.

The results bring out the fundamentally temporal-kinematic nature of the perceptual pattern of pushing. They appear difficult to reconcile with an interpretation based on past experience, but tally with the theory of “Ampliation of Movement” put forward by Michotte. According to this theory the essential point lies in the phenomenal transitory belonging to A (the moving object) of the movement performed by B (the projectile).     

After-images from retina and brain

The evidence pointing to the retinal origin of after-images is considered. The reports of the occurrence of after-images from visual images of hallucinatory vividness are reviewed.

Experimental results are presented to indicate that a complementarily coloured afterimage may arise following the exposure of the temporarily blind retina to a coloured stimulus.

After-images, or after-effects, from vivid images are described in seventeen persons (mostly possessors of “number-forms”). They are found to move with the eyes and to show, in some persons, a degree of conformity with Emmert's Law which, while considerable, is less than that of after-images of real stimuli. In the case of one “eidetic” subject, the after-images from neither real nor imaged stimuli conformed with Emmert's Law. In some persons, after-images of images occur in complementary colours.

The retinal origin of after-images is affirmed, but that they can occur occasionally as a purely central phenomenon is acknowledged. The possible learned or inherent nature of after-images of central origin is discussed.     

A study of position habits induced by reward and “frustration”

Predictions from Maier's theory of “frustration”-instigated behaviour have been tested in an experimental situation differing significantly from that in which the theory was propounded yet containing the central element of “frustration”—the insoluble problem.

A water discrimination unit was employed in which the performance of rats would be observed during attacks on insoluble problems, position problems or symbol problems.

Two groups, each containing ten Wistar albino rats, served as subjects. The research design consisted of the following phases: preliminary training, development of position responses, exposure to a symbol-reward problem with 50 per cent, punishment and exposure to a symbol-reward problem with 100 per cent, punishment. The design differed for the two groups only at the phase in which the position responses were established. During this phase one group was exposed to a position-reward problem and the other to an insoluble problem.

Position responses were established as frequently under position-“frustration” (position stereotypes) as under position-reward (position habits) conditions. Position stereotypes were more rigid—more resistant to extinction—than position habits under conditions of 50 per cent, punishment. Position stereotypes were as readily extinguished under 100 per cent, punishment as were position habits under 30 per cent, punishment.

The first two observations conform to predictions made from Maier's theory. The third does not. That is to say, not all situations containing the basic elements of “frustration” give rise to stereotyped behaviour patterns which are as rigid or “fixated” as Maier's theory would predict. It is a reasonable hypothesis that the characteristics of stereotyped responses established in certain “frustration” situations may be described adequately in terms of conventional learning principles without the necessity of resorting to a distinction between “goal-motivated” and “frustration-instigated” behaviour.     

Early motion processes and the kinetic depth effect

It has been known for over 30 years that motion information alone is sufficient to yield a vivid impression of three-dimensional object structure. For example, a computer simulation of a transparent sphere, the surface of which is randomly speckled with dots, gives no impression of depth when presented as a stationary pattern on a visual display. As soon as the sphere is made to rotate in a series of discrete steps or frames, its 3-D structure becomes apparent. Three experiments are described which use this stimulus, and find that depth perception in these conditions depends crucially on the spatial and temporal properties of the display:

1. Depth is seen reliably only for between-frame rotations of less than 15°, using two-frame and four-frame sequences.

2. Parametric observations using a wide range of frame durations and inter-frame intervals reveal that depth is seen only for inter-frame intervals below 80 msec and is optimal when the stimulus can be sampled at intervals of about 40-60 msec.

3. Monoptic presentation of two frames of the stimulus is sufficient to yield depth, but the impression is destroyed by dichoptic presentation.

These data are in close agreement with the observed limits of direction perception in experiments using “short-range” stimuli. It is concluded that depth perception in the motion display used in these experiments depends on the outputs of low-level or “short-range” motion detectors.     

The effect of an irrelevant dimension on “same-different” judgements of multi-dimensional stimuli

Subjects made “same”-“different” judgements of simultaneously presented pairs of visual stimuli which could vary either in shape and colour independently, or in shape alone. In both conditions only shape was relevant to the “same”-“different” judgement. In the former condition “same” and “different” reaction times (RTs) were shorter when the states (“same” or “different”) of the relevant and the irrelevant dimension, colour, were the same. This result is interpreted as support for either a perceptual or a response interference hypothesis. The presence of an irrelevant dimension did not appear to affect differentially “same” and “different” judgements. The need for a re-evaluation of the results from other studies of multi-dimensional stimulus discrimination is discussed.     

Divided attention, order of report and responses to immediately successive signals

Two effects, “divided-attention” and “order of report”, are operationally denned. Their relative contributions to the reduction in efficiency which accompanies the recognition of difficult nonverbal signals, presented simultaneously, is considered. Experiment I evaluated the two effects in the absence of a fixed order of report and emphasis instructions, confounding features of previous studies. The results showed: an overall impairment of performance with simultaneous signals; a contribution of both effects to the decrement, with a suggestion of the primacy of the “order of report” effect; and a significant interaction between the latter effect and modality, such that visual signals showed the greater effect. Experiment II using similar signals tested the assumption that simultaneity of presentation is a necessary condition for obtaining reduced efficiency with multiple signals. The assumption was only partially confirmed, a significant decrement in performance occurring only for the second of two successively presented signals. Similarities between the two sets of results are noted, as well as between these and modality differences obtained with verbal materials. Two possible accounts of the data are proposed, one based on “input”, the other on “storage” models of divided-attention. The hypothesis that subjects report the most clearly perceived signal first is rejected as an independent explanation.